Angle grinder is your right hand man with any metal work. There are grinding wheels, abrasive cutting discs, sanding wheels, sanding discs, wire wheels, wire cups, tons and tons of stuff. If you take the guard off, it gives you much much more freedom, but you have to be much much more conscious of what you're doing.
My primary use is digging out bad welds to replace them. Smoothing welded surfaces. Rounding sharp edges. List goes on